Slope Percentage Calculator
Enter the rise and run to find the slope as a percentage grade, with the angle and ratio.
Updated
Slope Percentage Calculator
Our Slope Percentage Calculator finds how steep a ramp, road, roof, driveway or trail is, as a percentage grade, from its rise and run. Along with the grade it shows the angle in degrees, the slope as a 1 : x ratio, the length along the slope and whether it goes uphill or downhill.
Quick answer
Slope percentage is rise ÷ run × 100, with both measured in the same unit: 5 ÷ 20 × 100 = 25%.
- 100% grade is a 45° slope, not a vertical wall
- Angle: arctan(rise ÷ run), so 25% ≈ 14.04°
- Ratio: 1 : 12 (a typical wheelchair ramp) ≈ 8.33%
- Downhill: a negative rise gives a negative grade, such as −25%
What Is Slope Percentage?
Slope percentage, also called grade or percent grade, says how many units a surface rises for every 100 units it runs horizontally. A 6% road climbs 6 m for every 100 m of horizontal distance.
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run
0% is flat. 100% means the rise equals the run, a 45° slope. A vertical wall has no finite grade, because the run is 0.
How to Calculate Slope Percentage
- Measure the rise, the vertical change in height. Use a negative number for downhill.
- Measure the run, the horizontal distance, in the same unit as the rise.
- Divide the rise by the run and multiply by 100.
Example: a driveway rises 5 ft over a horizontal 20 ft. 5 ÷ 20 = 0.25, and 0.25 × 100 = 25%. If the units differ, convert first: a rise of 30 cm over a run of 5 m is 0.3 m ÷ 5 m = 6%.
Slope Percentage to Degrees
Grade and angle are not proportional, so you cannot multiply or divide by a fixed number. Use the tangent:
grade = tan(angle) × 100
25% is arctan(0.25) ≈ 14.04°, and 30° is tan(30°) × 100 ≈ 57.74%. The Arctan Calculator and the Tangent Calculator do these steps on their own.
Slope Percentage Chart
| Grade | Angle | Ratio |
|---|---|---|
| 1% | 0.57° | 1 : 100 |
| 2% | 1.15° | 1 : 50 |
| 5% | 2.86° | 1 : 20 |
| 8.33% | 4.76° | 1 : 12 |
| 10% | 5.71° | 1 : 10 |
| 25% | 14.04° | 1 : 4 |
| 33.33% | 18.43° | 1 : 3 |
| 50% | 26.57° | 1 : 2 |
| 100% | 45° | 1 : 1 |
| 173.21% | 60° | 1 : 0.58 |
Grades above 100% are possible: they are slopes steeper than 45°.
Slope as a Ratio (1 : x)
Ramps and drainage are often given as a ratio of rise to run, such as 1 : 12 (1 unit up for every 12 across). To convert:
6% → 1 : (100 ÷ 6) ≈ 1 : 16.67
A bigger second number means a gentler slope. Roof pitch works the same way: a 4 in 12 pitch is 4 ÷ 12 ≈ 33.33%.
Slope Length
The run is measured flat, but a ramp or roof is longer than its run. Its length along the surface comes from Pythagoras:
√(5² + 20²) ≈ 20.62
The calculator shows this in the same unit as your inputs. A rise of 3 and a run of 4 gives a length of exactly 5.
Typical Slopes
- Wheelchair ramps: commonly 1 : 12 or gentler (8.33% or less), such as under the US ADA standards.
- Drainage: about 1% to 2% so water runs off flat-looking surfaces.
- Roads: main roads usually stay below about 6% to 8%; short local streets can be much steeper.
- Roofs: a 4 in 12 pitch is about 33%, and a 12 in 12 pitch is 100% (45°).
Local building codes set the actual limits, so check the rules that apply to your project.
Common Mistakes
- Thinking 100% is vertical. 100% is 45°; vertical is not a finite grade.
- Using the slope length as the run. The run is the flat distance, which is shorter.
- Mixing units. A rise in cm over a run in m gives an answer 100 times too big.
- Treating grade as degrees. 10% is about 5.71°, not 10°.
Key Terms
- Rise
- The vertical change in height.
- Run
- The horizontal distance covered.
- Grade
- Rise ÷ run × 100, as a percentage.
- Pitch
- Roof slope as rise per 12 units of run.
- Length
- The distance along the slope itself.
How to Use the Slope Percentage Calculator
- Enter the rise. Type the vertical change in height, such as 5. Use a negative number, such as −5, for a downhill slope.
- Enter the run. Type the horizontal distance in the same unit as the rise, such as 20. The run must be more than 0.
- Read and copy the slope. The grade appears as you type, with the working, the angle in degrees, the 1 : x ratio, the slope length and the direction. Press Copy to copy it, or Clear or Esc to start again.
Example: a ramp rising 1 ft over a 12 ft run. Enter 1 and 12. The grade is 8.333333%, with an angle of about 4.76°, a ratio of 1 : 12 and a slope length of about 12.04 ft.
Who Can Use This Calculator?
Frequently Asked Questions (FAQs)
How do you calculate slope percentage?
Divide the rise by the run and multiply by 100, using the same unit for both. A rise of 5 over a run of 20 is 5 ÷ 20 × 100 = 25%.
Is a 100% slope vertical?
No. A 100% slope rises 1 unit for every 1 unit of run, which is a 45° angle. A vertical wall has a run of 0, so its grade is not a finite number.
How do you convert slope percentage to degrees?
Take the arctangent of the grade divided by 100. 25% is arctan(0.25) ≈ 14.04°, and 10% is about 5.71°.
How do you convert degrees to slope percentage?
Take the tangent of the angle and multiply by 100. 30° is tan(30°) × 100 ≈ 57.74%, and 45° is 100%.
What is a 1:12 slope as a percentage?
A 1 : 12 slope is 1 ÷ 12 × 100 ≈ 8.33%, about 4.76°. It is a common maximum for wheelchair ramps.
What is a 2% slope?
A 2% slope rises or falls 2 units for every 100 units of horizontal distance, which is 1 : 50 or about 1.15°. It is often used for drainage.
Can slope percentage be more than 100%?
Yes. Any slope steeper than 45° has a grade over 100%. A 60° slope is about 173.21%.
What does a negative slope percentage mean?
It means the surface goes downhill in the direction you measured. A rise of −5 over a run of 20 is −25%.
Is slope percentage the same as grade?
Yes. Slope percentage, grade and percent grade all mean rise ÷ run × 100.
Is the Slope Percentage Calculator free?
Yes. It is completely free, needs no sign-up, and can be used as many times as you like.
Try our Slope Percentage Calculator to find the grade of any slope, with the angle, the ratio and the slope length.